I'm also getting inundated with angry customers unable to download their digital products because of this issue. As a (hopefully temporary) work-around, I have modified the e-mail notification that gets sent out to digital download customers, explaining the issue, and how to TEMPORARILY disable the "Safe Browsing" option in Chrome's security settings to enable the Zip file to be downloaded ... and then change it back. I include a screen-shot image of that specific page, and explain how they can navigate to that page. I also tell them if they aren't comfortable doing it that way, and they don't have access to a different browser like Edge, Firefox, Safari, etc, to contact me and I'll send them their product using something like We Transfer. It's not a very satisfying solution, and appears pretty "unprofessional", but it's the best I could come up with for now, and does seem to have greatly reduced the angry e-mails. btw, I tell them the way to get to the Chrome security settings screen is to open a new tab, and type "chrome://settings/security" in the URL bar.
The (somewhat) good news is I've had interaction with several of the "live chat" help desk folks about this over the past couple of days, and they all have said that "Squarespace engineers are looking into it", and "It is a priority issue". Assuming we can take them at their word about that, it's a much better response than "Not our problem" which was the initial response many folks seemed to have been getting early on.